Twisted-pair copper wires were initially designed to carry low-bandwidth voice telephone signals. Today, twisted-pair copper wires are widely used to carry high-bandwidth data signals from a central office (CO), a remote terminal (RT), or a distribution point (DP) to customer premises equipments (CPE) in digital subscriber line (DSL) systems. Asymmetric digital subscriber line (ADSL)/ADSL2/ADSL2+ described in “Asymmetric digital subscriber line (ADSL) transceivers,” International Telecommunications Union—Telecommunication Standardization Sector (ITU-T) document G.992.1, 1999, “Asymmetric digital subscriber line transceivers 2 (ADSL2),” ITU-T document G.992.3, 2002, and “Asymmetric digital subscriber line (ADSL) transceivers—Extended bandwidth ADSL2 (ADSL2+),” ITU-T document G.992.5, 2003, which are incorporated by reference, use a bandwidth of up to a few megahertz (MHz). Very-high speed digital subscriber line (VDSL)/VDSL2 described in “Very-high speed Digital Subscriber Line Transceivers 2 (VDSL2 draft),” ITU-T document G.993.2, July 2005, which is incorporated by reference, use a bandwidth of a few tens of MHz. Fast access to subscriber terminals (G.fast) described in the ITU standard “Fast Access to Subscriber Terminal,” ITU-T document G.9701, December 2014, which is incorporated by reference, uses a bandwidth of about 100 MHz or higher.